Microlithographic exposure apparatuses are used for producing microstructured components, such as integrated circuits or LCDs, for example. Such a projection exposure apparatus comprises an illumination device and a projection lens. In the microlithography process, the image of a mask (reticle) illuminated by the illumination device is projected with the aid of the projection lens onto a substrate (for example a silicon wafer) coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection lens, in order to transfer the mask structure to the light-sensitive layer.
The use of so-called fly's eye condensers for obtaining light mixing is conventional in the illumination device, said fly's eye condensers comprising grid arrangements made of a multiplicity of beam-deflecting elements (e.g. lens elements with dimensions in the millimeter range) for producing a multiplicity of optical channels. In principle, such a fly's eye condenser may be used both for field homogenization and pupil homogenization. Beyond the homogenization of the laser light, a further important object of the fly's eye condenser lies in stabilization in this case, meaning that the position of the illumination in a specific plane of the illumination device remains unchanged in relation to variations of location and, in particular, direction of the beams emanating from the laser light source.
In principle, it is desirable to minimize the number of employed optical elements (e.g. refractive lens elements in an illumination device configured for operation in the VUV range or in the case of an operating wavelength of more than 150 nm) during the operation of a microlithographic projection exposure apparatus.
However, in a conventional typical design of an illumination device equipped with a fly's eye condenser, as depicted schematically in FIG. 6, a beam path is realized which is collimated to the extent that the chief rays passing centrally through the respective optical channels (each of which, in accordance with FIG. 6, being formed by respectively one beam-deflecting optical element 611, 612, 613—also referred to as “field honeycomb” below—of a first beam-deflecting arrangement 610 and one beam-deflecting optical element 621, 622, 623—also referred to as “pupil honeycomb” below—of a second beam-deflecting arrangement 620) extend parallel to the optical system axis OA upon entry into the fly's eye condenser 600. A consequence of this in turn is that the virtual intermediate images produced by the beam-deflecting optical elements or “pupil honeycombs” 621, 622, 623 of the second beam-deflecting arrangement 620 lie—as indicated in FIG. 6 by dashed arrows—at “negative infinity” in relation to the light propagation direction. As likewise indicated in FIG. 6, the beam-deflecting optical elements or “field honeycombs” 611, 612, 613 of the first beam-deflecting arrangement 610 focus the illumination light into the optical channels in each case, with the images of the field honeycombs accordingly being recorded by an optical unit 614 from the intermediate image lying at “negative infinity” in relation to the light propagation direction and being imaged on a target surface 615, which is situated in the rear focal plane of the optical unit 614 and which may be e.g. a field plane of a reticle masking system (REMA).
The beam path described above on the basis of FIG. 6, which is collimated in the region of the fly's eye condenser 600 and in which there is a light entry perpendicular to the plane of the fly's eye condenser 600 or the first beam-deflecting arrangement 610 thereof, is selected, in particular, in order to prevent unwanted field dependencies of the intensity (in particular unwanted intensity variations of the illumination pupil over the field or variation of the illumination poles of a specific illumination setting, such as e.g. a dipole setting, on the reticle plane) which otherwise occur in the microlithographic imaging process and which are caused by the imaging properties of the beam-deflecting optical elements of the fly's eye condenser. Typically, optical systems such as, for example, a zoom-axicon system, are used in the illumination device for realizing this beam path which is collimated in the region of the fly's eye condenser 600, but this is accompanied by a transmission loss and therefore a reduction or impairment of the throughput of the projection exposure apparatus. Moreover, the beam path which is collimated in the region of the fly's eye condenser 600 is selected with the light entry perpendicular to the plane of the fly's eye condenser 600 or the first beam-deflecting arrangement 610 thereof in order to minimize a change in the system transmission as a consequence of variations in the direction of the beams emanating from the laser light source (also referred to as “pointing”) in conjunction with the finite angle divergence of the beams incident on the beam-deflecting optical elements or “field honeycombs” 611, 612, 613 of the fly's eye condenser 600.
In respect of the prior art, reference is made merely by way of example to U.S. Pat. No. 8,520,307 B2 and WO 2011/006710 A2.